Stable analysis on speed-adaptive observer in regenerating mode

Speed-adaptive full-order flux observer is the most promising flux estimator among all the sensorless control method. However, conventional speed-adaptive flux observer becomes unstable during regenerating operation at low speed since induction motor is an observable system except dc excitation. Thus, the instability problem is caused by inappropriate designing of observer. Based on the eigenvalues of extended observer, this paper interprets unstable situation, that the eigenvalues of extended observer have a positive real part. Therefore, the observer cannot converge. Against the two different solutions for unstable problem—positive real maintaining and current error augment, the proposed method based on the eigenvalue could unify these two solutions, which gives the complete stability condition for speed-adaptive full-order observer. It does a lot help in observer designing. The observer configured by this proposed method was verified in the torque controlling of 20 kW induction motor. According to the experiment result, with appropriate designing of observer, the unstable situation during regeneration mode could be completely overcome.